The Duke and Duchess of Cambridge look relaxed in their casual clothes during a visit to Blachford Lake in Canada

Kate and Wills may not have been spotted on the tandem Boris bike they received from the Mayor as a wedding present yet, but they are secret fans of the free bike scheme.The bright blue two-seater they own is probably the most conspicuous bicycle in London, so on their off-duty days the Duke and Duchess of Cambridge prefer to cycle side-by-side like the rest of us.

St James's Palace confirmed that the couple have been known to use the rental bikes.

Lost their love of tandem? William and Catherine canoeing on the same lake back in July

A spokesman said: 'The Duke and Duchess of Cambridge occasionally use the London cycle scheme bicycles to undertake private journeys around London.'

And who could blame them, the route from their home in Kensington Palace to their Office in St James' Palace can be cycled in 20 minutes.

It is a beautiful ride through Hyde Park and Green Park with a Boris bike docking station at each end and only the slightly tricky Hyde Park Corner to negotiate.

Mr Johnson first set the rumour treadmill rolling last week when he told LBC radio: 'I don't know for certain, but I was told that members of the royal family do use them.

'I was told that Wills and Kate use them but that may be inaccurate.'

On your bike: Eight million journeys have been made on Boris bikes since their launch in July 2010

Eight million journeys have been made on the bikes since the scheme was introduced in July 2010.